Antelope hung back to avoid horse (3)
I believe the answer is:
gnu
'antelope' is the definition.
(gnu is a kind of antelope)
'hung back to avoid horse' is the wordplay.
'back' says to take the final letters (the letter at the back).
'to avoid horse' becomes 'nu' (I can't explain this - if you can you should give a lot more credence to this answer).
The final letter of 'hung' is 'g'.
'g'+'nu'='GNU'
Can you help me to learn more?
(Other definitions for gnu that I've seen before include "Large African antelope" , "hitherto unknown, we hear" , "Large heavy antelope" , "Creature" , "Strange gun for an antelope" .)